1. Field of the Invention
The present invention relates to an oil seal which is a kind of a sealing device. For example, the oil seal of the present invention is used in a field relating to an automobile or in a field of a general purpose machine and the like.
2. Description of the Conventional Art
An oil seal is generally required to have low torque characteristics so as to suppress sliding abrasion of a seal lip. In order to obtain low torque characteristics, a technique for reducing fastening force by reducing a cross section of a seal lip or the like, and a technique for reducing a friction coefficient by change of a material, modification of a surface (for example, coating of a fluorine resin) and the like have been discussed. However, in order to realize more excellent low torque characteristics, it is considered to realize low torque characteristics based on fluid lubrication by increasing the thickness of an oil film on a sliding surface.
FIG. 6 illustrates a conventional technique developed. In this technique, screw sections 54 and 55 are provided on a slope 52 at the side of sealed fluid and a slope 53 at the side opposite to the sealed fluid of a seal lip 51 respectively, and a pumping effect induced by the screw sections 54 and 55 pushes back the sealed fluid toward the side of the sealed fluid (refer to Japanese Utility Model Application Laid-Open No. 3-29768).
According to this technique, since the pumping effect induced by screw sections 54 and 55 pushes back the sealed fluid toward the side of the sealed fluid, sealing property increases. However, since the thickness of the oil film on the sliding surface necessarily decreases, low torque characteristics based on fluid lubrication can not be realized.
Further, Japanese Patent Application Laid-Open No. 2003-254439 describes a technique, in which an intermediate surface is provided between a slope at the side of sealed fluid and a slope at the side opposite to the sealed fluid. However, this prior art is not to provide a reverse screw section on the intermediate surface.